Hammock (ecology)
Hammock is a term used in the southeastern United States for stands of trees, usually hardwood, that form an ecological island in a contrasting ecosystem. Hammocks grow on elevated areas, often just a few inches high, surrounded by wetlands that are too wet to support them. The term hammock is also applied to stands of hardwood trees growing on slopes between wetlands and drier uplands supporting a mixed or coniferous forest. Types of hammocks found in the United States include tropical hardwood hammocks, temperate hardwood hammocks, and maritime or coastal hammocks. Hammocks are also often classified as hydric (wet soil), mesic (moist soil) or xeric (dry soil). The types are not exclusive, but often grade into each other.
Unlike many ecosystems of the coastal plain of the southeastern United States, hammocks are not tolerant of fire. Hammocks tend to occur in locations where fire is not common, or where there is some protection from fire in neighboring ecosystems. Hammocks have begun developing in historic times in areas where fire has been suppressed through human intervention, or where elevations above wetlands have been created by dredging, mining, road and causeway building, and other human activities. On the other hand, many hammocks have been destroyed by development, as they often occur on higher land in desirable locations, such as barrier islands and other waterfront locations.[1]
The etymology of the term "hammock" is obscure. Dictionaries usually give it as an archaic form of "hummock" ("hammock" appeared in print earlier than "hummock"). "Hammock" is first attested in English in the 1550s as a nautical term for a tree-covered island (a mound of trees) seen on the horizon. "Hammock" is used to refer to stands of hardwood trees on the coastal plain from North Carolina to Mississippi.[2][3]
Tropical hardwood hammocks
In the United States, tropical hardwood hammocks are found in southern Florida. Sub-types of hammocks in southern Florida include rockland hammocks on the Miami Rock Ridge and in the Big Cypress National Preserve, Keys rockland hammocks in the Florida Keys, coastal berm hammocks in the Florida Keys and along the north shore of Florida Bay, tree island hammocks in the Everglades, shell mound hammocks, coastal rock barren hammocks in the Florida Keys, and sinkhole hammocks on the Miami Rock Ridge.[4]
The trees forming the canopy of the southernmost tropical hardwood hammocks in Florida are almost all West Indian species. The live oak (Quercus virginiana) is the only temperate hardwood species to appear regularly in such hammocks. Hammocks along the east coast of Florida as far north as Cape Canaveral, and along the west coast of Florida as far north as the mouth of the Manatee River on Tampa Bay, include West Indian species as canopy trees, but with increasing numbers of temperate species with increasing latitude, so that tropical hardwood hammocks grade into temperate hardwood hammocks.[1]
The tree island hammocks in the Everglades appear as teardrop-shaped islands shaped by the flow of water in the middle of the slough. Many tropical species such as mahogany (Swietenia mahagoni), gumbo limbo (Bursera simaruba), and cocoplum (Chrysobalanus icaco) grow alongside the more familiar temperate species of live oak (Quercus virginiana), red maple (Acer rubrum), and hackberry (Celtis laevigata).[5]
Temperate hardwood hammocks
Temperate hardwood hammocks are narrow bands of temperate broadleaf forest that occur on the coastal plain of the southeastern United States. In most of the southeast, including the Florida panhandle, the trees in temperate hardwood hammocks are primarily deciduous (southern hardwood forest). In the central part of the Florida peninsula hardwood hammocks are dominated by temperate evergreen hardwoods. Hardwood hammocks in northeastern Florida have a mixture of deciduous and evergreen trees, and hardwood hammocks in southern Florida north of the Everglades have a mixture of temperate evergreen and tropical trees.[6][7][8]
Maritime hammocks
Maritime hammocks, also known as maritime forests or coastal hammocks, are found on stable sand dunes away from the beach on barrier islands, and on small islands in salt marshes. They are found all along the Atlantic Coast and Gulf Coast of the United States. Some authorities classify coastal hammocks as hydric hammocks.[9][10][11][12]
Hydric hammocks
Hydric hammocks, also known as low hammocks, wetland hardwood hammocks, or lowland oak hammocks, grow on soils that are poorly drained or that have high water tables, subject to occasional flooding. They are usually found on gentle slopes just above swamps, marshes or wet prairies. Hydric hammocks are found in scattered locations in Florida north of Lake Okeechobee, with concentrations along the upper St. Johns River, the Atlantic coast of northeastern Florida, and particularly along the Big Bend section of the Gulf Coast of Florida, from Aripeka to St. Marks.[13]
Mesic hammocks
Mesic hammocks, also known as upland hardwood forest, upland mixed forest, upland hardwood hammock, oak hammock, or cabbage palm hammock, grow on moist soils that are rarely flooded. There is typically a dense layer of leaf litter, and the sandy soils are relatively rich. Mesic hammocks in the central part of the Florida peninsula have a lower diversity of tree species than do those to the north and south, as the ranges of most deciduous hardwoods found in northern Florida do not extend south of about Orlando, and the ranges of the tropical hardwoods found in southern Florida do not extend as far north as Lake Okeechobee.[14][15]
Cabbage palm-live oak hammocks
Cabbage palm-live oak hammocks, also known as prairie hammocks, are a sub-type of mesic hammocks composed principally of live oak and cabbage palm trees. They also occur in central and southern Florida in prairies and floodplains, on river levees, and on slopes between dry uplands and wetlands.[16][17]
Xeric hammocks
Xeric hammocks, also known as xeric forests, sand hammocks, live oak forests, oak woodlands, or oak hammocks, grow on old sand dunes that are very well drained. The most common canopy tree in xeric hammocks is the sand live oak, Quercus geminata. Other species of scrub oak and pine are also found in xeric hammocks. Plants that are typical of scrub or sandhill communities, particularly palmetto, are found under the canopy. Xeric hammocks are somewhat resistant to fire, but a fire that becomes established in a hammock will destroy it. [18][19][20]
See also
Notes
- ^ a b "Tropical Hardwood Hammock". Miami-Dade County. Retrieved 25 December 2011.
- ^ Harper, Roland M. (September 29, 1905). "'Hammock', 'Hommock' or 'Hummock'?" (PDF). Science. XXII (561): 400–402. Retrieved 25 December 2011.
- ^ Austin, Daniel F. (1983). "Hammocks" (PDF). Palmetto. 3 (1): 4. Retrieved 25 December 2011.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ "Tropical Hardwood Hammock". Croc Docs - University of Florida Research and Education Center. Retrieved 24 December 2011.
- ^ "Ecosystems: Hardwood Hammock". National Park Service. Retrieved 24 December 2011.
- ^ Valentine, James and D. Bruce Means (2006). Florida Magnificent Wilderness: State Lands, Parks, and Natural Areas. Sarasota, Florida: Pineapple Press. p. 30. ISBN 978-1-56164-361-5.
- ^ Whitney, Eleanor Noss, D. Bruce Means, Anne Rudloe. Priceless Florida: natural ecosystems and native species. Sarasota, Florida: Pineapple Press. p. 86. ISBN 978-1-56164-308-0. Retrieved 24 December 2011.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ "Temperate Hardwood Forests". University of Florida IFAS Extension. Retrieved 24 December 2011.
- ^ "Maritime Hammock Habitats". Smithsonian Institution. Retrieved 24 December 2011.
- ^ Fabrizio, Laura and Maria S. Calvi (2003). "Georgia's Marsh Hammocks: A biological survey" (PDF). Southern Environmental Law Center. p. 5. Retrieved 24 December 2011.
- ^ "Marsh Environments: Coastal Hammocks, Oyster Bars, and Salt Barrens". United States Geological Survey. Retrieved 24 December 2011.
- ^ "Florida Ecological Restoration Inventory - Hardwood Hammocks and Forests". Florida Department of Environmental Protection. Retrieved 2 January 2012.
- ^ Vince, Susan W., Stephen R. Humphrey and Robert W. Simmons (1989). The ecology of hydric hammocks: a community profile (PDF). Washington, D.C.: U. S. Fish and Wildlife Service Biological Report 85 (7.26). pp. 1–3. Retrieved 26 December 2011.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Duever, Linda Conway (1998). "Mesic Hammock" (PDF). Palmetto. 8 (2): 4–5. Retrieved 2 January 2012.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ "Mesic Temperate Hammock" (PDF). U.S. Fish and Wildlife Service. Retrieved 2 January 2012.
- ^ "Mesic Temperate Hammock". Croc Docs - University of Florida Research and Education Center. Retrieved 24 December 2011.
- ^ "Hardwood Hammock Forest" (PDF). Florida Fish and Wildlife Conservation Commission. Retrieved 2 January 2012.
- ^ "Xeric Hammock" (PDF). Florida Natural Areas Inventory. Retrieved 31 December 2011.
- ^ "Xeric Hammock". University of Florida: Ordway-Swisher Biological Station. Retrieved 31 December 2011.
- ^ "Woodland Habitat: Xeric Hammocks". Friends of the Enchanted Forest. Retrieved 31 December 2011.